Genetically modified crops have led to a significant increase (not a reduction as promised) in the use of herbicides, according to the journal Environmental Sciences Europe. Herbicide and insecticide use decreased for the first few years after these crops were introduced in1996. However, herbicide application then began to steadily increase, which outstrips the much smaller decrease in insecticide usage. Now, in 2012, many farmers are spraying about 25% more herbicide on each acre of their genetically modified crops than they would if they were planting conventional varieties.

Some GMO crops have been spliced with a gene that is resistant to both bugs and the Monsanto weedkiller Roundup, generically called glyphosate. Farmers have been spraying their crops with glyphosate to kill the weeds without killing the crops; however, the glyphosate-resistant weeds have developed a resistance. Farmers growing genetically modified crops are now forced to use other, older chemicals to kill the weeds. Charles Benbrook is worried about one in particular, 2,4-D, which has been linked with birth defects, reproductive problems and certain cancers. "The more farmers try to spray their way out of this corner they've backed themselves into, the worse it's going to get," Benbrook said. (Charles Benbrook, researcher at Washington State University, Seattle Times, Maureen O'Hagan, October 2012)

Many consumers are concerned that GMO food may have unforeseen effects on human health.